The present invention relates to a slide fastener and more particularly to a waterproof slide fastener.
A waterproof slide fastener including a pair of left and right fastener stringers is known. The fastener stringers comprise a pair of left and right waterproof slide tapes and a plurality of fastener elements, which are formed by injection-molding synthetic resin material on the side ends of the slide tapes opposite to each other. Between the left and right fastener stringers, a slider is slidably inserted for engaging and disengaging the left and right elements with and from each other. Further, the slide fastener is constructed such that a bottom stopper and a top stopper are provided to the lower end and the upper end of the fastener elements, respectively, by synthetic resin material. The technique to injection-mold a bottom stopper using synthetic resin is disclosed in JP,H02-107309,U etc. In such a slide fastener, each of the fastener elements includes an engaging head, a base, a neck for connecting between the engaging head and the base, and a pair of shoulders which extend from both sides of the head in the shape of wing pieces. Each engaging head has two front and rear protrusions which protrude from the opposite side end of a fastener tape. Then, by engaging the left and right fastener elements vertically adjacent to each other using the slider, a shoulder of one of the fastener elements is fitted between the two front and rear protrusions (into a fitting groove in the above JP,H02-107309,U) of the other fastener element. In addition, the opposite faces of the left and right fastener tapes are brought into tight contact with each other. Thereby, the left and right fastener stringers are sealed fluid-tight between them, bringing about the waterproof property.
However, since there is no fastener element in a region between the lowest fastener element and the bottom stopper, a force of fastener elements engaging with each other is not generated. Therefore, in the region, a contacting force between the left and right fastener tapes is weak as compared with that in a region where the fastener elements are engaged with each other. For this reason, when a water pressure or the like is applied, there is a case that water or the like can leak from the region between the lowest fastener element and the bottom stopper. To prevent such water leakage, JP,2007-215819,A discloses a technique in which the region between the lowest fastener element and the bottom stopper is sealed with a waterproof sheet member. As another means, a technique is known that when the bottom stopper is injection-molded, one or more lower fastener elements are covered so as to improve the waterproof property around the bottom stopper.
[Patent Document 1] JP,H02-107309,U
[Patent Document 2] JP,2007-215819,A
However, in the slide fastener described in the patent document 2, there is a case that the sheet member comes off because of long period use. On the other hand, in a method to cover lower fastener elements with the bottom stopper, there is a case that a molten resin leaks upward from a die through a gap between the two front and rear protrusions of the engaging head of a fastener element because of the pressure at injection molding. Such a leakage can cause burrs and make the production of a slide fastener difficult. Further, leaked resin can disturb the engagement and disengagement between lower fastener elements. To completely prevent a leakage from a die as the bottom stopper is injection-molded, the die must be produced with very high precision. In this case, the production cost of a slide fastener becomes excessively high.
In view of the foregoing problems, the invention provides a slide fastener that can improve the waterproof property near the bottom stopper cost-effectively.